Despite the presence of a vigorous and broadly reactive HIV-1 specific CTL response in infected individuals, progression to AIDS almost inevitably occurs. The factors that allow disease progression in the setting of this strong CTL response have not been well defined. One hypothesis suggests that mutations within critical epitopes may allow HIV-1 to escape immune recognition by cytotoxic T lymphocytes. In this case the ability of the host to generate new CTL responses may be a critical factor in containing viral replication. Another hypothesis suggests that the deletion of HIV-specific CTL clones over the course of disease i.e. "clonal exhaustion" may be a factor explaining the decline in CTL activity that accompanies disease progression. We have developed methods to sequence the T cell receptor genes of HIV-1-specific CTL and have shown that the vigorous CTL response in an infected individual may be due to an oligoclonal expansion of effector cells that can persist for several years. We have also found instances in which HIV-1 variation within CTL epitopes leads to a loss of recognition by CTL previously isolated from that individual, yet the majority of the CTL response remains directed at a minor in vivo sequece variant. Our ability to follow population of particular HIV epitope-specific CTL by the analysis of their TCR usage will allow us to determine the fate of these cells over the course of infection. The purpose of the experiments in this proposal is to use T cell receptor (TCR) sequence analysis as a means to assess the diversity of the CTL response to known HIV-1 epitopes and to assess variation of HIV-1 sequences within these epitopes in patients with different disease courses. Our aim is to test the following hypotheses: a) A broadly directed HIV-specific CTL response, against multiple HIV epitopes correlates with slow disease progression. b) The vigorous CTL responses in subjects with non-progressing illness will be mediated by a population of CTL clones with heterogeneous TCR that are better able to cope with HIV-1 sequence variation. c) If HIV-1 sequence variation exists within these epitopes in these subjects, CTL populations exist that are able to recognize these variants, indicating an ability to response to HIV variation. Specifically we propose to 1) Determine the epitope specifically and TCR heterogeneity of HIV-specific CTL clones in persons matched at three or more class I alleles but with different disease states and viral loads. 2) Determine the longevity of - defined clonal responses by measuring CTL precursor frequency and by probing TCR cDNA libraries with specific oligonucleotide probes. 3) Correlate the magnitude and heterogeneity of specific clonal responses with the in vivo virus present in persons with different disease outcomes. Understanding the contribution of the HIV-1- specific CTL response to long-term non progressing infection may lead to practical strategies to augment this arm of the immune response.